Conventionally, technology where a pair of hydrostatic transmissions (HSTs) are laterally connected, driving axles project laterally from respective HSTs, running-driving wheels are fixed to the outer ends of both axles, wherein movable swash plates as capacity adjusting members for the hydraulic pumps of the HSTs are individually changed in angle thereby driving the left and right running wheels individually, is well-known, as disclosed in, for example, the U.S. Pat. No. 4,782,650.
In such construction, running speeds of the left and right HSTs, when the vehicle is driven straight forward, are equalized, and, when turned, are different.
The above-said vehicle, however, could not travel straight-forward unless the output rotations of left and right HSTs completely coincided with each other, adjustments in shipment took much time, and parts and assembly errors had to be diminished so as to improve accuracy. Also, when there was a difference between the capacities of hydraulic pumps and motors, left or right turning feeling of the vehicle was different, resulting in that the vehicle was very hard to steer.
Also, the same vehicle was larger in turning radius due to its lateral arrangement of the pair of HSTs, so that the vehicle had to run in the same place many times for such work as lown-mowing around trees, thereby deteriorating the working efficiency.
Thus, for overcoming the above problems, a vehicle including a steering operation means; a pair of running-driving axles; a pair of running wheels drivingly connected with the pair of running-driving axles; a first differential unit interposed between the pair of running-driving axles; a first hydrostatic transmission for transmitting a driving force to the first differential unit; a pair of steering output shafts; a second differential unit interposed between the pair of steering output shafts; a second hydrostatic transmission for transmitting a driving force to the second differential unit; a first drive train interposed between one of the steering output shafts and one of the running-driving axles, and a second drive train interposed between the other steering output shaft and the other running-driving axle for transmitting the rotating effort to the other running-driving axle in the opposite direction to the first drive train, wherein the second hydrostatic transmission operationally interlocks with the steering operation means so that the output speed and direction of the second hydraulic transmission is changed by manipulation of the steering operation means, has come to be invented. The vehicle does not require such labor as above mentioned for precise coincidence between the capacities of the first and second hydrostatic pumps and motors. Also, when both the hydrostatic pumps and motors are arranged in a longitudinal line, the vehicle becomes laterally compact, thereby diminishing the turning radius.
However, it is still desirable to improve the running efficiency of the vehicle when it is driven on a rough road or a soft ground. Also, when such a vehicle has a plurality of running wheels arranged in a longitudinal direction so as to be made larger in whole length, it is still difficult to diminish the turning radius of the vehicle only by changing the number of rotations of the left and right running-driving wheels.
The present invention relates to a vehicle comprising at least six running wheels and a transmission which, when a steering operation means is manipulated, differentially drives a pair of running-driving axles so as to make a vehicle turn left and right.
An object of the present invention is to provide a vehicle improved in its running efficiency on rough or soft ground and in its turning on a small circle, wherein a transmission drivingly connected with a prime mover applies composite force of equal first rotational forces in the same directions and equal second rotational forces in the opposite directions onto a pair of running-driving axles differentially connected with each other. A speed change operation means and a steering operation means are manipulated so as to regulate the directions and magnitudes of the first rotational forces and the second rotational forces respectively.
To attain the object, the vehicle of the present invention comprises at least six running wheels, i.e., a pair of first running wheels serving as running-driving wheels attached onto respective running-driving axles, a pair of second running wheels disposed before or behind the pair of first running wheels so as to be laterally turnable into the running direction of the vehicle, and a pair of third running wheels disposed before or behind the pair of first running wheels.
Especially, the pair of second running wheels may be castors so as to secure a reduced turning circle for the vehicle.
Furthermore, the pair of third running wheels may be castors.
Also, the pair of third running wheels may be attached to a pair of second axles disposed in parallel to the pair of first running-driving axles. In this case, the driving force of the first running-driving axles may be transmitted to the second axles. Especially, the running-driven axles may be driven through a pair of power transmission mechanisms interposed between the respective running-driving axles and the respecive second axles so as to rotate the pair of second axles in the same rotational direction of the running-driving axles, thereby enhancing the running efficiency on rough or soft ground.
These and other objects of the invention will become more apparent in the detailed description and examples which follow.